"The Hoa were highly represented in Vietnam's business and commerce sector before the Fall of Saigon in 1975. As of 2012, they comprise a well-established middle class ethnic group and make up a high percentage of Vietnam's educated and upper class."

Regression to The mean? The test scores are for 15 year olds in 2012, so people born in 1996-97. But that IQ 94 you cited presumably is for the entire adult population, which would include a lot of people who grew up during the war and may have been malnourished as children which I imagine would have a long-term depressive effect on IQ. So that 94 number may be artificially low.

I did a comprehensive review of intelligence and achievement data for Vietnam on my Human Varieties blog in 2013.

The Vietnamese secondary students tested for PISA 2012 were a relatively elite sample, and Vietnam also had one of the worst attrition rates of participating nations.

Further, I think that there could be corruption in how the remaining one-party Socialist states present themselves to the world. I've also shown that Cuba suspiciously overperforms on international tests. I haven't formally reviewed China, but I also don't think the Shanghai PISA scores are a good representation of the current population intelligence. (Lynn has a new review of national IQs which I have not yet seen, but the older books did not accurately report China's IQ data.)

Finally, the evidence for IQ in Vietnam is tricky, possibly suggesting higher (near European average) scores during adolescence. Which would at least be a little more consistent with the PISA results.

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